Architects and engineers must take into account the effects not only of seismic movement, but also those movements caused by building sway, settlement, thermal expansion and contraction. Architects know that any building that may be subjected to ground oscillations must be designed to control and accommodate movement caused by resonation within the structure while additionally providing for tower sway, thermal movement and settlement.
Buildings have been designed with various expansion joints between the walls, ceilings and floors to take into account the sway, ground motion, settlement, etc. associated with buildings. However, a disadvantage of the use of expansion joints is that they create a chimney effect in the building structure. Because fire is an everpresent danger in association with any building and the chimney effect at unprotected expansion joints may actually advance a spread, it is highly desirable to utilize a fire barrier in conjunction with any expansion joint assembly to provide additional protection to aid in the prevention of the spreading of any fire.
Fire barriers are often comprised of a suitable fire retardant material reinforced with wire mesh and/or foils. This metal reinforcement is positioned between the joint prior to the application of the expansion joint assembly. The fire barrier is a highly thermal resistant material which protects the joint from the associated chimney effect within the building construction.
Other types of joint treatment systems have included insulated metal foil (i.e. aluminum) layers such as those disclosed in the Fire Resistant Directory, pages 718-721 and 821-823. While these fire resistant barrier layers are suitable for reduction in the chimney effect associated with buildings containing expansion joints, they clearly can be improved. For example, these barrier structures are difficult to install and difficult to handle and ship.
Fire barrier devices have also been designed that comprise flexible, composite barriers including a laminate of intumescent material and a backing material, such as metal foils or sheets, paper, plastic, cloth, or a mat of inorganic fibers in a binder. When exposed to heat or fire, the intumescent materials expand so as the fill open spaces in the vicinity of the architectural joint to prevent the passage of smoke, fire, water or gas.
These systems have conventionally been required to be affixed to the structural joint members by fire resistant caulk compositions. During installation of the fire barrier, a caulking is applied to the edges of the barrier to provide a seal to the structural building elements.
These systems are recognized in the industry as being messy and difficult to install. Further, great care must be taken to assure that the caulk bead is of sufficient quality and quantity to hold the fire barrier and to provide the seal. Due to the nuisance caused by these installation difficulties, the integrity of these systems may be compromised by worker frustration.
A further drawback of the caulk adhered systems is the physical rigidity or inflexibility of the caulk material, and its low tolerance for compensating for building movement. In both fire testing and real life cycling of fire barriers affixed with caulk, both the caulk and the integrity of the barrier are significantly compromised. This is recognized by the fact that the U.L. Standard for Tests For Fire Resistance of Building Joint Systems (UL2079), which requires cycling of the building joint systems for a minimum of twenty complete movement cycles prior to the fire test, waives the cycling requirement for the caulk adhered fire barrier systems. The caulk adhered systems are thus "like new" when tested, unlike other systems which must be cycled and "conditioned" (or aged).